How to create an app?

I have designed all of the pages however don't know what the next step is.

The app requires users to be able to create their own group, then generate a code to allow friends to join the same group. I know that I need some sort of list manager to store the data but I don't know where to start.

In addition it needs to be able to send emails and send push notifications.

The requirement needed by you is 100% coding practices to follow and you will get more accurate answers from stackoverflow. Just start away with alphabets and refer questions through Google. Definitely you will keep progressing.

I didn't said Warrior Forum can't answer this question. I said you will get more better and coding examples of different aspects when similarly search through Google and Stackoverflow.. Just you have to start your coding.

You are either going to have to learn web programming or hire someone.

Your project is going to involve Post submissions from forms saved to a database and associations within that database that link certain users to certain groups. It will also need actions and listening for events to send emails etc.

The good news is that though learning programming still requires time and commitment to learning its not as hard as several years ago. A good framework (Rails for Ruby or Laravel for PHP) will give you a lot that you need.

send emails and send push notificationsThere are lots of resource for notification,just you have to arrange customized code as like your needs and connect notification cloud directory such as Firebase.

If you are serious about that app better hire someone.There is no way you can put any quality in it with your level of programming skills.If you don't want to hire or learn , you can find a way to sell designs if you are good at that.